Sensing of the electrical parameters of asynchronous motors (ASMs) is important for field-oriented regulation of the motors that are produced.
Although field-oriented regulation (FOR) of asynchronous motors is known, its vulnerability or sensitivity to changes in parameters represents a problem that has not satisfactorily been solved. In FOR, regulation takes place in a coordinate system oriented on the rotor-flux space-vector, so that the flux-forming and torque-forming current components can be influenced separately. The instantaneous position and instantaneous absolute value of the rotor-flux space-vector are usually determined with the aid of an analog or digital software model of the motor. All the rotor-flux estimating methods which are based upon a model have the disadvantage, however, that the parallel model can correctly reproduce the motor state only when the parameter values used in the software model agree with the instantaneous parameter values in the particular motor being operated.
During operation, the stator resistance and rotor resistance can change by up to 50% as a function of temperature. Changes in main inductance must be compensated for when the ASM is also operated in the field-weakening region.